Cytology generally refers to the study of the structure, function and pathology of cells. In a clinical laboratory environment cytotechnologists and pathologists diagnose a patient's condition by visually examining specimens of the patient's cells. These cells are typically stained to better define the structure of the cells and to aid in the visual review of the cells.
One common cytological technique is a pap smear, in which the cells from a woman's cervix are sampled and analyzed in order to detect the presence of abnormal cells. The process involves collecting a specimen from a woman's cervix using a brush or related instruments, and the specimen is then transferred to a slide for subsequent processing. The slide containing the specimen is then stained using on or more staining solutions and the slides are then coverslipped. The slide can then be evaluated visually by a cytotechnologist or by an automated imaging system.
One of the commonly used stains for cytological analyses is the Hematoxylin stain. Hematoxylin, itself, is not a dye but is a natural compound extracted by boiling the wood of the South American and West Indian logwood tree (Haematoxylon campechianum), and partly purified by recrystallization. To become a dye, the hematoxylin first needs to be oxidized to form haematein, either through exposure to air and sunlight or UV light or by employing various agents such as including potassium permanganate, iodine, sodium iodate, sodium periodate, potassium periodate, hydrogen peroxide or mercuric oxide.
However, even at this stage except for a few applications, direct staining with haematein is usually unsuccessful and it is necessary to include various metallic salts, or mordants for the stain to work effectively. The combination of mordant and dye is known as a “lake” and in the case of haematein-mordant such lakes are often positively charged, behaving as cationic dyes at low pH. For the purposes of clarity and uniformity of terms, the haematein-mordant lake shall be referred to hereinafter as a hematoxylin stain or hematoxylin staining solution.
Hematoxylin stains bind to acidic components of a cell such as nuclear chromatin, mitotic spindles, fibrin, and other cellular components. The color of the stained structures depends on the various mordants used to make the hematoxylin stain. Potassium alum, the most common mordant, gives the stained structures a blue to purple color.
The present invention relates to a means for improving the shelf-life of a nuclear staining solution. In particular, the method of the present invention is related to adding an antioxidant to a hematoxylin staining solution which maintains the performance of the stain over its shelf-life.